Substrate having fine line, electron source and image display apparatus

ABSTRACT

As a substrate having a fine line and capable of suppressing crack generation in the substrate and peeling of the fine line, the invention discloses a configuration in which plural recesses are arranged on the fine line, and particularly a configuration in which the interval of the plural recesses does not exceed 200 μm. There is also disclosed a configuration in which the plural recesses are arranged along a direction crossing the longitudinal direction of the fine line.

This application is a division of application Ser. No. 10/637,624, filedAug. 11, 2003, which is a division of application Ser. No. 10/014,398,filed Dec. 14, 2001, now U.S. Pat. No. 6,621,207.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a substrate having a fine line, anelectron beam substrate utilizing the same, and an image displayapparatus employing the same.

2. Related Background Art

There are also known configurations in which a fine line is formed on asubstrate. The fine line can be, for example, a cell partition wallbetween light-emitting cells in a plasma display panel, or a wiring(electrode) for driving a device on a substrate.

In the following there will be shown an example of forming a fine lineas a wiring in an electron source substrate.

As the electron source, there is for example known a configurationutilizing a surface conduction electron-emitting device. FIGS. 13A and13B are respectively a schematic plan view of an electron emittingdevice and a schematic cross-sectional view along a line 13B-13B in FIG.13A.

As shown in FIGS. 13A and 13B, the electron emitting device isprincipally composed of an insulating substrate 200, electrodes 2, 3formed by film formation on the substrate 200, an electron-emittingelectroconductive film 7 formed by film formation so as to beelectrically connected to the electrodes 2, 3, and an electron-emittingregion 8 provided in the electron-emitting electroconductive film 7.

As an application of such electron-emitting device, there is known animage forming apparatus such as a display apparatus. FIG. 14 is apartially broken perspective view of an image forming apparatus (imagedisplay apparatus) utilizing the surface conduction electron-emittingdevice shown in FIGS. 13A and 13B.

As shown in FIG. 14, such image display apparatus is provided with asubstrate 81, an outer frame 82 and a face plate 86 on which an imageforming member (phosphor) 84 is provided, and such outer frame 82,substrate 81 and face plate 86 are sealed at the connecting portionsthereof with an unrepresented adhesive material such as low-meltingglass frit to constitute an envelope (hermetic container) 88 formaintaining the interior of the image display apparatus in vacuum state.

On the substrate 81, there is fixed a substrate 200 on whichelectron-emitting devices are formed. On the substrate 200,electron-emitting devices 74 are formed in a matrix arrange n×m, whereinn and m and positive integers at least equal to 2, and are suitablyselected according to the desired number of display pixels.

Each electron-emitting device 74 is connected to a row-direction wiring4 and a column-direction wiring 6, both consisting of electroconductivefilms. The wirings shown in FIG. 14 consist of n column-directionwirings 6 and m row-direction wirings 4 (also called “matrix wirings”).At the crossing region of the row-direction wiring 4 and thecolumn-direction wiring 6 there is provided an unrepresented insulatinglayer to insulate the row-direction wiring 4 from the column-directionwiring.

In order to form the image display apparatus described above, it isnecessary to form a plurality of the row-direction wirings 4 and thecolumn-direction wirings 6.

For forming a plurality of the row-direction wirings 4 and thecolumn-direction wirings 6, it is disclosed, for example in the JapanesePatent Application Laid-open No. 8-34110, to form the wiring composed ofan electroconductive film by a printing technology that is relativelyinexpensive and is capable of covering a large area without a vacuumapparatus or the like.

For such printing technology, there is usually employed screen printing.

In the screen printing technology, a plate having an aperture of thedesired pattern is employed as a mask, and paste containingelectroconductive particles such as metal particles is printed throughthe aperture of the mask onto a substrate constituting the object ofprinting and is then baked thereby obtaining an electroconductive wiringof the desired pattern.

Also in order to obtain a finer pattern or an improvement in thepositional precision which are difficult to attain with the screenprinting, there may also be employed a method of employingphotosensitive metal paste formed by providing the paste withphotosensitive property.

In the method employing such photosensitive metal paste, thephotosensitive paste formed as a film on the substrate is exposed tolight through a photomask having a desired wiring pattern and is thensubjected to development and baking processes thereby forming anelectroconductive wiring of the desired pattern.

Among the electron-emitting devices, in addition to the aforementionedsurface conduction type electron-emitting device, there are also known,for example, a spint type electron-emitting device having a conicalelectron-emitting region, and a MIM type electron-emitting device. Theelectron-emitting device can be utilized as an image display device by acombination with a phosphor which emits light by the electrons emittedby such electron-emitting device. Among the image display devices, thereis known, for example, an EL device in addition to the electron-emittingdevice. Also there is known a configuration in which a micromirror isutilized as an image display device and an image is displayed byintegrating such micromirrors and controlling the light reflection byeach of such micromirrors. Also there is already widely employed aconfiguration of utilizing liquid crystal as an image display device fordisplaying an image.

Another background technology is disclosed in the Japanese Utility ModelApplication Laid-open No. 5-38874, which discloses, for connectingmutually opposed two conductive films, a technology of superposing aresistive film with each end of the two conductive films. Also there isdisclosed a technology of forming the end portion of the conductive filmwith a straight or curved folding line such as of a sawtooth shape, acomb-tooth shape or an undulating shape in order to prevent a rack inthe resistive film at the stepped difference in the superposed regionfrom growing into a large single crack.

Still another background technology is disclosed in the Japanese PatentApplication Laid-open No. 8-315723 which discloses a configuration offorming a recess in the wiring and positioning a spacer in such recess.

SUMMARY OF THE INVENTION

Formation of a fine line, such as a wiring, consisting of a thick filmfor example by a printing method on a substrate is associated with thefollowing drawbacks.

In a configuration in which the fine line is formed on the substrate,such fine line may be peeled off from the substrate.

Such phenomenon is considered to result from generation of a stressbetween the fine line and the substrate.

For example, in the case a wiring formed on a glass substrate is madethick, a crack may be formed in the glass substrate in a region wherethe end of the wiring is in contact with the substrate (such crack beinghereinafter called an end crack). Also a crack may be generated in theglass substrate in a direction parallel to the longitudinal direction ofthe wiring (such crack being hereinafter called a side crack).

One of the causes of such phenomena is that, in case an organiccomponent is contained in the composition, such organic componentescapes at the baking operation to induce a contraction in the volume,thereby applying a stress to the glass substrate. Another cause isassumed that a stress is applied to the glass substrate by a thermalstress resulting from the difference in the thermal expansioncoefficient between the components of the paste and the glass substrate.

Such cracks are formed at the baking process or with the lapse of timethereafter.

Also there may result drawbacks that the aforementioned end crack andside crack respectively extend and are mutually connected to form alarge crack or that the wiring itself becomes bent and is peeled offfrom the substrate.

Such situations will be explained further with reference to FIGS. 15A to15D, schematically showing the drawbacks resulting from the wiringsubstrate of the conventional technology. FIGS. 15A to 15D schematicallyshow a wiring formed on a substrate, wherein FIG. 15A is a plan view,FIG. 15B is an enlarged perspective view, seen from the rear side, of acircled portion 15B in FIG. 15A, FIG. 15C is a magnified look-throughview, seen from the rear side, of encircled portion 15C in FIG. 15A, andFIG. 15D is a cross-sectional view along a line 15D-15D in FIG. 15A.

The illustrated example shows a case where plural slat-shaped(line-shaped) thick film wirings 1 are formed (baked) on the glasssubstrate 200.

As shown in FIG. 15B (a magnified look-through view of an encircledportion 15B), side cracks 30 may be generated in the glass substrate200, substantially parallel to the longitudinal direction of the wiring1 and along both ends of the width thereof.

Such side crack 30 principally depends on the film thickness and theprobability of crack generation becomes higher as the film thicknessincreases. The cross-sectional shape of the wiring is also aninfluencing factor. In case of employing photosensitive paste, thecross-sectional shape of the wiring is substantially trapezoidal, butthe both lateral faces becomes somewhat thicker than the centralportion. For this reason, there are often generated two side cracksslightly inside both ends of the width of the wiring as illustrated.

Also as shown in FIG. 15C (a magnified look-through view of an encircledportion 15C), end cracks may be generated with a shell-shaped pattern atthe end of the wiring. Also such end crack 30 depends on the filmthickness and the probability of crack generation becomes higher as thefilm thickness increases.

Also, as shown in FIG. 15D, both end portions 5 of the wiring 1 may bepeeled off in a large dimension. The probability of such phenomenonbecomes higher as the film thickness increases or as the number ofbaking process increases.

In case a stress (for example thermal expansion or contraction mentionedabove or volume contraction) is applied to the wiring 1, since thewiring 1 is adhered thereto, a tensile force or the like is transmittedto the substrate 200 thus leading to a crack if the adhesive force islarge or a peeling if the adhesive force is small.

The aforementioned crack or peeling of wiring tends to be generated whenthe film thickness after baking is at about 10 μm, and the probabilityof generation of such crack or peeling and the level thereof becomeshigher as the film thickness increases for example to 12 μm or 18 μm.

Such end crack or peeling of wiring leads, in the lead portion of thewiring, to a drawback that a flexible circuit board or a tab cannot bemounted by peeling thereof together with the wiring at the succeedingmounting operation of such flexible circuit board or tab, or, in otherportion, a drawback of shortcircuiting resulting from that the endportion of the wiring is bent up to come in contact with other portionsor resulting from the chipping or dropping of the wiring, or a drawbackthat the shape of markers such as an alignment mark becomes unstable.

The present application discloses an invention of which an effect is tosuppress the peeling of the fine line and the crack generation in thesubstrate.

One of the inventions relating to the substrate having the fine line ofthe present application is featured by:

-   -   a substrate having a fine line, wherein the fine line is        provided, in at least a part in the longitudinal direction        thereof, with plural recesses arranged with a gap not exceeding        200 μm.

The presence of such recess allows to disperse the stress generated inthe fine line or at the interface between the fine line and thesubstrate.

In particular, the aforementioned plural recesses are preferablyarranged in a direction crossing the longitudinal direction of the fineline (namely a direction not parallel to the longitudinal direction ofthe fine line, and the gap between the end of the fine line and therecess adjacent to such end does not exceed 200 μm in a directionpassing through the plural recesses and perpendicular to thelongitudinal direction of the fine line. Wherein, the above “pluralrecesses are arranged in a direction crossing the longitudinal directionof the fine line” means a configuration that the plural recesses arearranged in a sectional area along the direction crossing the longitudeof the fine line. Such configuration of the structure is for exampleshown in FIGS. 1A, 1B, 1E and 1F.

Also in the aforementioned invention, between the recesses and/orbetween the end of the fine line and the recess in a direction passingthrough the recesses and perpendicular to the longitudinal direction ofthe fine line there exists a portion thicker than the thickness of therecess (namely the distance between the bottom of the recess and thesurface of the substrate on which the fine line is formed), and suchthickness of the recess preferably does not exceed 15 μm, morepreferably 10 μm. Also the thickness of the recess is preferably atleast equal to 30 nm.

Also in the aforementioned invention, there can be advantageouslyadopted a configuration in which the aforementioned recess is formed asa groove extending in the longitudinal direction of the fine line and aconfiguration in which such groove is arranged in plural units inmutually parallel manner.

The aforementioned invention can be particularly advantageously appliedto a configuration where the aforementioned fine line is utilized as awiring.

Also the aforementioned invention is particularly effective in case thefine line is obtained by applying paste-like material onto the substrateand then heating such material.

The present application also includes the following invention:

-   -   a substrate having a fine line, wherein the fine line is        provided with a recess in at least a part thereof, wherein the        width of the fine line in a direction passing through the recess        and perpendicular to the longitudinal direction of the fine line        is 200 μm or larger.

This invention may be advantageously used in combination with theforegoing inventions.

The present application further includes the following invention:

-   -   a substrate having a fine line, wherein the fine line is        provided in at least a part in the longitudinal direction        thereof, with plural recesses arranged in a direction crossing        the longitudinal direction of the fine line.

Also this invention may be advantageously used in combination with theforegoing inventions.

In the foregoing inventions, the recess is preferably provided in allthe portion of the fine line where the width of the fine line, in adirection perpendicular to the longitudinal direction thereof, is 200 μmor larger, but it may also be provided only in a particularly necessaryportion such as the longitudinal end portion of the fine line. Forexample the longitudinal end of the fine line is apt to be subjected toan external force by a succeeding process such as connection to anothermember and therefore tends to generate peeling, so that theconfiguration having the recess of the present invention can beadvantageously adopted.

Also the present application includes an invention for a configurationin which the fine line provided on the substrate is utilized as a wiringfor driving an electron-emitting device. More specifically, suchconfiguration can be realized by providing an electron-emitting deviceon the aforementioned substrate, electrically connecting the fine line,constituting the wiring, with the electron-emitting device and supplyinga voltage for causing the electron-emitting device to emit electronsthrough the wiring.

Furthermore, the present application includes an invention for aconfiguration in which the aforementioned electron source is combinedwith a phosphor emitting light by the electrons emitted by theelectron-emitting device to constitute an image display apparatus.

Furthermore the present application includes an invention for a methodfor forming a wiring on a substrate, the method comprising:

-   -   a step of forming a film of photosensitive electroconductive        paste to constituting the wiring;    -   a step of irradiating the formed film of the electroconductive        paste with light through a photomask bearing a pattern similar        in shape to the recess to be formed on the surface of the        wiring;    -   a development step after the light irradiation; and    -   a baking step after the development step.

Also the wiring forming method of the present invention comprises:

-   -   a step of printing conductive paste on the substrate, utilizing        a plate bearing a pattern similar in shape to the recess to be        formed on the surface of the wiring; and    -   a baking step after the printing.

Also the wiring forming method of the present invention comprises:

-   -   a step of forming a wiring on the substrate; and    -   a step of eliminating a part of the formed wiring thereby        forming a recess.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, 1D, 1E, 1F and 1G are schematic views showing wiringsubstrates constituting embodiments and examples of the presentinvention;

FIG. 2 is a schematic plan view showing a state in which a wiring isformed on a substrate;

FIGS. 3A, 3B, 3C and 3D are views showing process steps for forming awiring on a substrate;

FIGS. 4A and 4B are respectively a plan view and a cross-sectional viewshowing a state where an insulation layer is formed;

FIGS. 5A and 5B are respectively a plan view and a cross-sectional viewshowing a state where an upper wiring is formed;

FIGS. 6A, 6B and 6C are views showing process steps of a wiring formingmethod in an example 2;

FIGS. 7A, 7B and 7C are views showing process steps of a wiring formingmethod in an example 3;

FIGS. 8 and 9 are views showing steps of a wiring forming method in anexample 4;

FIGS. 10A, 10B, 10C, 10D, 10E and 10F are views showing process steps ofa wiring forming method in an example 5;

FIGS. 11A, 11B, 11C, 11D, 11E and 11F are views showing process steps ofa wiring forming method in an example 6;

FIGS. 12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12I, 12J, 12K and 12L areviews showing process steps of a wiring forming method in an example 7;

FIGS. 13A and 13B are schematic views showing an electron-emittingdevice;

FIG. 14 is a partially cut-off perspective view of an image formingapparatus;

FIG. 15A, 15B, 15C and 15D are schematic views showing the drawbacks ina wiring substrate of conventional technology;

FIGS. 16A, 16B, 17A, 17B, 18A and 18B are views showing producingprocesses for an electron source substrate;

FIG. 19 is a partially cut-off perspective view of an image formingapparatus; and

FIG. 20 is a view showing the configuration in which a recess is formedin the lead portion of a wiring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now the present invention will be clarified by preferred embodimentsthereof, with reference to the accompanying drawings. However thedimension, material, form and relative arrangement of the componentsdescribed in such embodiments are not intended to limit the presentinvention to such description unless otherwise specified.

In the following embodiments, there will be described an example ofproviding a substrate with a wiring for driving an electron-emittingdevice, but the present invention is not limited to such example asexplained in the foregoing.

In the following there will be explained, with reference to FIGS. 1A to1G, an embodiment of a wiring substrate applicable for example to anelectron source substrate to be employed in an image forming apparatussuch as an image display apparatus. FIGS. 1A to 1G are schematic viewsof a wiring substrate embodying the present invention.

As shown in FIGS. 1A to 1G, the wiring substrate embodying the presentinvention is provided with a board 13 and a wiring 11 formed thereon,and, on the surface of the wiring 11, there is formed a groove 12 as arecess.

The “wiring” means an electroconductive structured member formed withdesired width, film thickness and length on a desired base member(hereinafter “substrate” will be used in the same meaning as thesubstrate).

As explained in the foregoing, on the surface of the wiring 11, there isformed a notch 12 as a recess.

Such notch 12 can assume various shapes (patterns seen from above) asshown in FIGS. 1A to 1F.

The notch 12 thus formed on each wiring 11 can disperse the stressgenerated therein, whereby the force of the wiring acting on thesubstrate 13 is weakened, thereby suppressing the generation of theaforementioned side crack and end crack and also suppressing thegeneration of the peeling. Particularly an array of plural notches canadvantageously disperse the stress.

Also, when the wiring is seen from above in planar manner, the notch 12may have a linear shape such as a continuous straight line, a brokenline or a curved line, or an individually independent shape (such as apattern of small circles). Also the direction of the notch 12 may or maynot be along the longitudinal direction of the substrate. Furthermore,the cross-sectional shape (in vertical cross section) of the notch 12may be a V shape of an acute angle, a U shape or an undulating shape.

The notch 12 is more preferably so formed that the extending directionthereof is substantially parallel to the longitudinal direction of thewiring or forms an angle not exceeding 45° with the longitudinaldirection of the wiring (hereinafter “direction substantially parallelto the longitudinal direction” and “direction forming an angle notexceeding 45° with the longitudinal direction” will be collectivelycalled “direction along the longitudinal direction”) and/or that a notchdoes not extend from a lateral end of the wiring to the other lateralend, since the electrical conductivity is not significantly hindered incase a fine line is used as a wiring. The longitudinal direction of thefine line (wiring) means the direction of the length if the fine linehas a form of a straight line. In case the fine line is curved or has abent portion, the longitudinal direction also becomes curved or bent.Also in case the paired lateral ends of the fine line are not parallelat least in a part thereof (for example a portion where the width of thefine line varies), the direction connecting the middle points of theopposed lateral ends is considered as the longitudinal direction.

The present inventors have made intensive investigation on the gap andthickness of the notch 12. As a result, it is confirmed that thegeneration of the side crack or end crack in the substrate can besuppressed in case the gap of the notches is 200 μm or less and thethickness of the notch is 15 μm or less for the thickness of the wiringwithin a range from several micrometers to several tens of micrometers.

The “gap of notches (recesses)” means the partition (thickness of thewiring (fine line) material itself) between a notch and a notch adjacentthereto.

Also the “thickness of notch (recess)” means the distance from thesurface of the substrate on. which the wiring (fine line) is formed tothe bottom of the notch. More specifically, it means the thickness ofthe wiring (fine line) material itself between the surface of thesubstrate and the bottom of the notch.

Furthermore, the generation of the aforementioned cracks can besuppressed with a high probability if the gap of the notches does notexceed 100 μm, more preferably 10 μm.

However, the presence of a notch in the fine line used as the wiringreduces the cross sectional area thereof, thereby increasing theresistance of the wiring. Therefore, from the standpoint of electricconductivity, the thickness of the notch is preferably as large aspossible.

In consideration of the foregoing, in case of forming a thin metal filmon the substrate so as not to hinder the electric conductivity, there isat least required a thickness of 30 nm for such film to serve as acontinuous film capable of maintaining the electrical conductivity.Therefore the fine line can serve as a substantially continuous wiringif the thickness of the notches is 30 nm or larger over thesubstantially entire surface of the wiring.

Such wiring can be formed on the substrate in various methods.

An example of the preferred forming methods is a printing methodutilizing photosensitive electroconductive paste.

Such method utilizing the photosensitive electroconductive pasteconsists of forming a film of the photosensitive electroconductive pasteon the substrate, then preparing a photomask bearing. patterns similarin shape to the notches, and irradiating the photosensitiveelectroconductive paste with light through the photomask, therebyforming the wiring with notches through subsequent steps such asdevelopment and baking.

In this method, adjustment may be made on the line width of the notchpattern on the photomask, the gap between the photomask and thephotosensitive electroconductive paste formed on the base member at thelight irradiation and the development condition of the photosensitiveelectroconductive paste to adjust the thickness of the finally formednotch within the aforementioned range.

Another example of the preferred forming methods is a screen printingmethod.

Such screen printing method consists of preparing in advance a platebearing a pattern similar in shape to the notch with predetermined widthand gap, then causing the plate to discharge electroconductive paste toconstitute the wiring thereby forming a pattern on the substrate andforming the wiring provided with the notch through processes such asbaking.

Also in this method, adjustment may be made on the line width of thenotch pattern on the plate and the process conditions for example in theprinting operation to adjust the thickness of the finally formed notchwithin the predetermined range.

As still another example of the preferred forming methods, it is alsopossible, after the formation of a wiring pattern without notch, topartially remove the wiring pattern for example by irradiating thewiring pattern with a laser light thereby forming the wiring with notch.

In such operation, the “wiring pattern” may be that prior to baking orthat after baking.

As explained in the foregoing, the crack in the substrate or the peelingof the wiring may be generated by the baking operation, but suchphenomenon may appear by only one baking or only after plural bakingoperations in case of forming plural film layers depending on thematerials to be used. Consequently there can be a situation where thenotch can be formed without any problem after the baking operation.

For example in the forming method utilizing photosensitive paste, thewiring pattern formed after the exposure with the conventional photomaskwithout the notch pattern and the development may be subjected to thelight irradiation prior to or after the baking.

Also in the screen printing method, the wiring pattern formed byprinting may be subjected to the light irradiation prior to or after thebaking.

Also in the aforementioned examples of wiring formation such as themethod utilizing the photosensitive electroconductive paste, the screenprinting method, the method of partially eliminating the wiring or amethod utilizing combination thereof, in case the desired film thicknessis obtained by executing the formation of the wiring in plural layers,it is also possible to form the notch from a layer positioned above thefinal film thickness of 30 nm or to a position above the final filmthickness of 30 nm.

In the aforementioned electroconductive paste, the principal componentis preferably composed of electroconductive particles such as of metal,and more preferably of a single material or mixed materials of arelatively low specific resistivity suitable for use in the wiring, suchas copper or silver. The electroconductive paste employing silverparticles as the electroconductive particles is advantageous since itshows satisfactory printing property and can be used without particularattention on the atmosphere of baking.

Also in the photosensitive electroconductive paste, theelectroconductive paste to which the photosensitivity is to be providedis preferably similar to the aforementioned electroconductive paste.

Also the wiring of the present invention is preferably applied to awiring substrate in which the film thickness of the wiring (fine line)is at least equal to 5 μm after baking, because the probability ofgeneration of the aforementioned end crack or side crack becomes higherwhen the film thickness exceeds about 5 μm. However, the fine line ofthe present invention is provided with a recess and is naturally thickerin a portion other than such recess. For example, if the thickness ofthe recess is 10 μm, a non-recess portion adjacent thereto is thickerthan 10 μm.

The wiring and wiring substrate of the aforementioned embodiment of thepresent invention are preferably applicable to an electron sourcesubstrate bearing plural electron-emitting devices and driving wiringstherefor, formed in a large scale on a substrate, and also to an imageforming apparatus utilizing such electron source substrate.

In the following there will be explained more specific examples based onthe above-described embodiment.

EXAMPLE 1

The example 1 has a configuration, among the aforementioned embodiments,identical with that shown in FIGS. 1A to 1G, wherein a notch 12, awiring 11 and a substrate 13 are shown.

FIG. 1A shows an example in which the notch 12 is formed in continuousmanner in a direction along the wiring (substantially parallel to thelongitudinal direction of the wiring), FIG. 1B shows an example in whichthe notch 12 is formed in non-continuous manner in a direction along thewiring (substantially parallel to the longitudinal direction of thewiring), FIG. 1C shows an example in which the notch 12 is formed incontinuous manner in a direction substantially perpendicular to thelongitudinal direction of the wiring, FIG. 1D shows an example in whichthe notch 12 is formed in non-continuous manner in a directionsubstantially perpendicular to the longitudinal direction of the wiring,FIG. 1E shows an example in which the notch 12 is formed in continuousmanner with an acute angle (45°) to the longitudinal direction of thewiring, and FIG. 1F shows an example in which the notch 12 is formed innon-continuous manner with an acute angle (45°) to the longitudinaldirection of the wiring, thus representing specific examples of thewiring with notch of the present invention.

FIG. 1G is a cross-sectional view seen from a direction indicated by anarrow in each of FIGS. 1A to 1F. In FIG. 1G, the gap of the notches isrepresented by “W”, and the thickness of the notch (distance from thesubstrate surface to the notch bottom as explained in the foregoing) isrepresented by “T”.

In any of the wiring patterns in FIGS. 1A to 1F, the gap “W” of thenotches is selected as 100 μm or less and the thickness is selectedwithin a range from 30 nm to 10 μm.

In the following there will be explained, with reference to FIGS. 2 to5B, a case of applying the wiring substrate to an image formingapparatus, namely employing it as an electron source substrate. Morespecifically, there will be explained a case of forming, as the wiringpattern for the image forming apparatus, a lower wiring and an upperwiring on the substrate thereby constructing a matrix wiring.

In these drawings, there are shown a wiring 11 formed on a substrate 13and constituting the lower wiring, and a notch 12 to be formed on thesurface of the wiring 11 in a manner described in the foregoing.

Also there are shown photosensitive electroconductive paste 14 used asthe material for the wiring 11, an upper wiring 17, an insulation layer16 for insulating the wiring 11 from the upper wiring 17, a screen plate18, an exposing light 19 and a mask 23.

FIG. 2 shows a state after the formation of the wiring 11, and FIGS. 3Ato 3D show the steps of formation (corresponding to a cross sectionalong a line 3-3 in FIG. 2). FIG. 3A is a 3-3 cross-sectional view afterthe film formation of the photosensitive electroconductive paste on thesubstrate 13, FIG. 3B is a 3-3 cross-sectional view at exposure, FIG. 3Cis a 3-3 cross-sectional view after development, and FIG. 3D is a 3-3cross-sectional view after baking.

FIGS. 4A and 4B are respectively a plan view and a cross-sectional viewalong a line 4B-4B in FIG. 4A, showing a state after the formation ofthe insulation layer 16. FIGS. 5A and 5B are respectively a plan viewand a cross-sectional view along a line 5B-5B in FIG. 5A, showing astate after the formation of the upper wiring 17.

At first there will be explained the method for forming the lower wiring11 on the substrate 13.

Referring to FIG. 3A, there were prepared a soda lime glass substrateand a quartz substrate as the substrate 13, and a film of thephotosensitive electroconductive paste 14 was formed by screen printingmethod on each substrate 13.

The photosensitive electroconductive paste 14, principally composed ofsilver particles, contained the silver particles in 60 to 80% and aglass component, a photosensitive material, glass frit and a solventcomponent in 20 to 4.0.

The film was formed with a screen plate of 150 mesh. The mesh X meansthat the screen has X screen apertures per side in a square of a side of25.4 mm.

Then drying was executed at about 80° C. to 150° C. in order to dry thephotosensitive electroconductive paste 14. The film thickness after thedrying was about 30 μm (FIG. 3A).

In the following there will be explained an exposure step with referenceto FIG. 3B.

In the present example, there was employed a mask 23 having a patternconsisting of two slits of a gap of 100 μm and a line width of 20 μm, inorder to form a notch 12 in the wiring pattern of a width of 300 μm asshown in FIG. 1A.

The mask is also provided, in other portions, with several trial slitsof the patterns as shown in FIGS. 1B, 1C, 1D, 1E and 1F, and was soaligned as to execute exposure on desired positions, and thephotosensitive electroconductive paste 14 was thus exposed to light(FIG. 3B).

In this operation, as shown in FIG. 3B, the photosensitiveelectroconductive paste 14 was exposed to the exposing light (laserlight) through the aperture of the mask, but a portion to constitute thenotch is not exposed because of the slit pattern.

Then the photosensitive electroconductive paste in the unexposed portionwas removed by development. The area where the notch is to be formed wasnot sufficiently exposed and is therefore partly eliminated in thedevelopment, whereby the notch was formed (FIG. 3C).

Then a baking step was executed at about 500° C. As the pattern showscertain shrinkage by the baking process, there could be obtained thelower wiring 11 with a wiring width of 280 μm, a wiring height of 15 μm,a gap between notches not exceeding 100 μm and a thickness of notch notexceeding 10 μm (FIG. 3D).

Then, as shown in FIGS. 4A and 4B, photosensitive insulating paste wasapplied in four layers, then exposed and developed to form theinsulation layer 16.

Then the upper wiring 17 was formed by a screen printing method.

In the screen printing, there were employed electroconductive pastecontaining silver particles in 60 to 80%, and a screen plate 18 of 150mesh.

The screen plate 18 was provided with a pattern consisting of two slitsof a gap of 100 μm and a line width of 50 μm, in order to form a notchin the wiring pattern of a width of 300 μm as shown in FIG. 1A. Theplate was also provided, in other portions, with several trial slits ofthe patterns as shown in FIGS. 1B, 1C, 1D, 1E and 1F, and such plate wasused to execute printing in the desired positions.

Then drying was executed at about 80° c. to 150° C. in order to dry theelectroconductive paste. The film thickness after the drying was about30 μm.

In the screen printing method, since the paste is discharged from thepattern of the plate, the actually printed ink becomes continuous by theink flow at the printing and drying despite the notch-forming slit beingas wide as 50 μm, thereby generating surface irregularities on thewiring pattern to form, through the baking process, the upper wiring 17with notch as shown in FIG. 5B.

Then a baking step was executed at about 420° C. As the pattern showscertain shrinkage by the baking process, there could be obtained theupper wiring 17 with a wiring width of about 280 to 290 μm, a wiringheight of about 18 μm, a gap between notches not exceeding 100 μm and athickness of notch not exceeding 10 μm.

In this manner there were prepared, on the substrate, the lower wiring11 with notch and the upper wiring 17 with notch positioned across theinterlayer insulation layer 16, thus completing a matrix wiring.

With the wiring with notch of the present example, regardless of thekind of the substrate, namely neither of the substrates employed showedany side crack, end crack or peeling of wiring.

Also any of the patterns shown in FIGS. 1A to 1F could be formed in asimilar manner, but the measured wiring resistance was lower in a notchpattern along the longitudinal direction of the wiring as shown in FIG.1A than in a notch pattern in a substantially perpendicular pattern, andis therefore advantageous for the basic requirement of minimizing theresistance of the wiring.

EXAMPLE 2

The present example shows a case of forming the wiring on the substratein a method different from that of the example 1. FIGS. 6A to 6C showthe process steps of the wiring forming method of the example 2, whereinshown are a substrate 13, a developed pattern 15, an exposing light(laser light) 19, and a completed wiring 11.

In the following there will be explained the process steps insuccession. In the present example, the materials employed are same asthose in the foregoing example 1, and the process is basically same, upto the development step, as that of the example 1. However the mask tobe used in the exposing step was free from the slit for constituting thenotch pattern. FIG. 6A shows a state after the development step in thismanner.

Then, as shown in FIG. 6B, the developed pattern was subjected toirradiation with a laser light having a spot of about 10 μm. The laserlight irradiation was executed so as to form notches with a gap thereofof about 100 μm and a thickness thereof of about 10 μm, utilizing asecond harmonic wave (wavelength 532 nm) of a YAG laser.

Then the pattern was baked in a baking condition similar to that in theexample 1 as shown in FIG. 6C thereby forming a wiring with notch. Asthe pattern shows certain shrinkage by the baking process, there couldbe obtained the wiring 11 with a wiring width of 280 μm, a wiring heightof 15 μm, a gap between notches not exceeding 100 μm and a thickness ofnotch not exceeding 10 μm.

Then there were prepared, on thus prepared lower wiring, an interlayerinsulation layer and an upper wiring with notch in a process similar tothat in the example 1, thus completing a matrix wiring.

The wiring prepared in the method of the present example providedeffects similar to those in the example 1. The present example alsoprovides an advantage of forming an arbitrary notch pattern in anarbitrary position (improved precision of forming position) since thenotch is formed by the laser.

Also as another method there was tried a method of preparing the notchwith the laser after the baking of the wiring, and such method providedan effect of suppressing the peeling of wiring in the extended elapse oftime.

EXAMPLE 3

The present example shows a case of forming the wiring on the substratein a method different from that of the example 1. FIGS. 7A to 7C showthe process steps of the wiring forming method of the example 3, whereinshown are a substrate 13, a printed pattern 15 a, an exposing light(laser light) 19, and a completed wiring 11.

In the following there will be explained the process steps insuccession. In the present example, a print pattern 15 a was printed onthe substrate by a method same as that (screen printing) employed in thepreparation of the upper wiring in the example 1 (FIG. 7A). However theplate used in the printing step was different from that in the example 1and was free from the notch pattern.

Then, as shown in FIG. 7B, the print pattern was subjected toirradiation with a laser light having a spot of about 10 μm. The laserlight irradiation was executed so as to form notches with a gap thereofof about 100 μm and a thickness thereof of about 10 μm, utilizing asecond harmonic wave (wavelength 532 nm) of a YAG laser.

Then the pattern was baked in a baking condition similar to that in theexample 1 as shown in FIG. 6C thereby forming a wiring with notch. Asthe pattern shows certain shrinkage by the baking process, there couldbe obtained the wiring 11 with a wiring width of 280 to 290 μm, a wiringheight of 18 μm, a gap between notches not exceeding 100 μm and athickness of notch not exceeding 10 μm.

Then there were prepared, on thus prepared lower wiring, an interlayerinsulation layer and an upper wiring with notch in a process similar tothat in the example 1, thus completing a matrix wiring.

The wiring prepared in the method of the present example providedeffects similar to those in the example 1. The present example alsoprovides an advantage of forming an arbitrary notch pattern in anarbitrary position (improved precision of forming position) since thenotch is formed by the laser.

Also as another method there was tried a method of preparing the notchwith the laser after the baking of the wiring, and such method providedan effect of suppressing the peeling of wiring in the extended elapse oftime.

EXAMPLE 4

The present example shows a case of forming the wiring on the substratein a method different from that of the example 1. FIGS. 8 and 9 show theprocess steps of the wiring forming method of the example 4, whereinshown are a substrate 13, a thin conductive film 20, a thick film wiring21, and a completed wiring 11.

In the following there will be explained the process steps insuccession. The present example prepares a lower wiring and an upperwiring on the substrate in a method basically same as that in theexample 1, thereby forming a matrix wiring, assuming the wiring patternof the image forming apparatus.

In the present example, in contrast to the foregoing example 1, prior tothe formation of the lower wiring, a conductive thin film 20 is formedby a photolithographic thin film etching method as shown in FIGS. 8 and9.

The conductive thin film 20 in the present example was composed of Pt ofa thickness of about 50 nm with Ti as a subbing layer. The subsequentsteps were conducted as in the example 1 to form a thick film wiring 21with paste, and to complete a wiring (lower wiring) 11 by integratingthe conductive thin film 20 and the thick film wiring 21. Then therewere prepared an interlayer insulation layer and an upper wiring withnotch in a process similar to that in the example 1, thus completing amatrix wiring on the substrate.

The matrix wiring prepared in the method of the present example,including the conductive thin film in the lower wiring, provided effectssimilar to those in the example 1. The present example also provides aspecific advantage that the wiring is never disconnected by the notch,since the notch is stopped at the surface of the conductive thin film 20even if the notch is formed locally over the entire thickness of thethick film wiring as shown in FIG. 9 for example by a defect in theprocess.

EXAMPLE 5

FIGS. 10A to 10F are views showing process steps of a wiring formingmethod of an example 5.

In the present example, the wiring is formed with plural layers in orderto further increase the thickness of the wiring.

In the drawings, there are shown a substrate 13, a photomask 23′, aphotomask 23 without the notch pattern, a developed pattern 15, exposinglight 19, and a completed wiring 11.

In the following there will be explained the process steps insuccession. As the present example employs steps basically same as thoseof the example 1 (utilizing photosensitive paste), the followingexplanation principally describes the points different from the example1.

In the present example, however, in order to form the wiring in twolayers, there are executed in succession a film forming step (FIG. 10A),an exposure step (FIG. 10B), a film forming step (FIG. 10C) and anexposure step (FIG. 10D) and then executed are a development step (FIG.10E) and a baking step (FIG. 10F) to form a thick film wiring.

In the present example, the first film forming step (FIG. 10A) wasexecuted with a screen plate of 325 mesh to obtain a dried filmthickness of 14 μm, and the succeeding exposure step (FIG. 10B) wasconducted with the photomask 23 without the notch pattern.

Then the second film forming step (FIG. 10C) was executed with a screenplate of 325 mesh to obtain an additional dried film thickness of 22 μmor a total thickness of 36 m, and the succeeding exposure step (FIG.10D) was conducted with the photomask 23′ having the notch pattern.

Through the subsequent development and baking steps, there was obtaineda wiring with notch, having a final film thickness of 18 (=7+11) μm witha thickness of the notch of 7 μm.

As the pattern shows certain shrinkage by the baking process, therecould be obtained the wiring 11 with a wiring width of 280 μm, a wiringheight of 18 μm, a gap between notches not exceeding 100 μm and athickness of notch not exceeding 10 μm.

Then there were prepared, on thus prepared lower wiring, an interlayerinsulation layer and an upper wiring with notch in a process similar tothat in the example 1, thus completing a matrix wiring.

The method of the present example enables the formation of the wiring ofa larger film thickness, without generation of cracks in the substrateor peeling of the wiring.

EXAMPLE 6

FIGS. 11A to 11F are views showing process steps of a wiring formingmethod of an example 6.

In the present example, the wiring is formed with plural layers in orderto further increase the thickness of the wiring.

In the drawings, there are shown a substrate 13, a photomask 23, adeveloped pattern 15, exposing light 19, and a completed wiring 11.

In the following there will be explained the process steps insuccession. As the present example employs steps basically same as thoseof the examples 1 and 5 (utilizing photosensitive paste), the followingexplanation principally describes the points different from the examples1 and 5.

In order to form the wiring in two layers as in the example 5, there areexecuted in succession a film forming step (FIG. 11A), an exposure step(FIG. 11B), a film forming step (FIG. 11C) and an exposure step (FIG.11D) and then executed are a development step (FIG. 11E) and a bakingstep (FIG. 11F) to form a thick film wiring.

In the present example, the first film forming step (FIG. 11A) wasexecuted with a screen plate of 200 mesh to obtain a dried filmthickness of 22 μm, and the succeeding exposure step (FIG. 11B) wasconducted with the photomask 23 having the notch pattern, similar tothat in the example 1.

In this operation, the distance between the exposed article and thephotomask (hereinaftere called “exposure gap”) was selected at about 300μm, in order that the notch pattern of a small line width is hardlyresolved to the bottom of the exposed article.

Then the second film forming step (FIG. 11C) was executed with a screenplate of 200 mesh to obtain an additional dried film thickness of 22 μmor a total thickness of 44 μm, and the succeeding exposure step (FIG.11D) was conducted with the photomask 23′ having the notch pattern as inthe example 1.

The exposure gap in this step was selected smaller than that for thefirst layer, being executed in a state close to the contact exposure, soas to achieve resolution to the bottom of the exposed article.

Through the subsequent development and baking steps, there was obtaineda wiring with notch, having a final film thickness of 22 (=11+11) μmwith a thickness of the notch of about 7 μm, wherein the notch wasformed as an unresolved pattern because of the larger exposure gap inthe first exposure step.

As the pattern shows certain shrinkage by the baking process, therecould be obtained the wiring 11 with a wiring width of 280 μm, a wiringheight of 22 μm, a gap between notches not exceeding 100 μm and athickness of notch not exceeding 10 μm.

Then there were prepared, on thus prepared lower wiring, an interlayerinsulation layer and an upper wiring with notch in a process similar tothat in the example 1, thus completing a matrix wiring.

The method of the present example enables the formation of the wiring ofa larger film thickness, without generation of cracks in the substrateor peeling of the wiring.

EXAMPLE 7

FIGS. 12A to 12L are views showing process steps of a wiring formingmethod of an example 7.

In the present example, the wiring is formed with plural layers (morespecifically in four layers) in order to further increase the thicknessof the wiring.

In the drawings, there are shown a substrate 12, a photomask 23, adeveloped pattern 15, a wiring 31 after baking, and a completed wiring11.

In the following there will be explained the process steps insuccession. As the present example employs steps basically same as thoseof the examples 1, 5 and 6 (utilizing photosensitive paste), thefollowing explanation principally describes the points different fromthe examples 1, 5 and 6.

In the present example, in order to form the wiring in four layers,there are executed in succession a film forming step (FIG. 12A), anexposure step (FIG. 12B), a film forming step (FIG. 12C) and an exposurestep (FIG. 12D) and then executed are a development step (FIG. 12E) anda baking step (FIG. 12F). Then there are executed a film forming step(FIG. 12G), an exposure step (FIG. 12H), a film forming step (FIG. 12I)and an exposure step (FIG. 12J) and then executed are a development step(FIG. 12K) and a baking step (FIG. 12L). In this manner there is formeda wiring thicker than in the example 5 or 6.

In the present example, the first film forming step (FIG. 12A) wasexecuted with a screen plate of 325 mesh to obtain a dried filmthickness of 14 μm, and the succeeding exposure step (FIG. 12B) wasconducted with a photomask (not shown) without the notch pattern(similar to the photomask 23 of the example 5).

Then the second film forming step (FIG. 12C) was executed with a screenplate of 325 mesh to obtain an additional dried film thickness of 14 μmor a total thickness of 28 μm, and the succeeding exposure step (FIG.12D) was conducted with a photomask (not shown) without the notchpattern (similar to the photomask 23 in the example 5).

Then the development and baking steps were executed to obtain a finalfilm thickness after baking of 14 (=7+7) μm.

Then the third film forming step (FIG. 12G) was executed with a screenplate of 325 mesh to obtain a dried film thickness of 14 μm on the bakedfilm of the first and second layers, and the succeeding exposure step(FIG. 12H) was conducted with a photomask (not shown) having the notchpattern (similar to the photomask 23 in the example 5).

Then the fourth film forming step (FIG. 12I) was executed with a screenplate of 325 mesh to obtain an additional dried film thickness of 14 μmor a total thickness of 28 μm on the baked film of the first and secondlayers, and the succeeding exposure step (FIG. 12J) was conducted with aphotomask (not shown) having the notch pattern (similar to the photomask23′ in the example 5).

Then the development and baking steps (FIGS. 12K and 12L) were executedto obtain a final film thickness after baking of 28 (=7+7+7+7) μm.

In the present example, the thickness of the notch is determined at theinterface between the third layer formed with the mask having the notchpattern and the second layer formed with the mask without the notchpattern, and there could be formed a wiring with a thickness of thenotch of about 14 μm.

As the pattern shows certain shrinkage by the subsequent baking process,there could be obtained the wiring 11 with a wiring width of 280 μm, awiring height of 22 μm, a gap between notches not exceeding 100 μm and athickness of notch not exceeding 15 μm.

Then there were prepared, on thus prepared lower wiring, an interlayerinsulation layer and an upper wiring with notch in a process similar tothat in the example 1, thus completing a matrix wiring.

The method of the present example enables the formation of the wiring ofa larger film thickness, without generation of cracks in the substrateor peeling of the wiring.

In particular, since the film thickness is increased by film formationwith plural layers employing a screen plate of 325 mesh providing arelatively limited film thickness in a single film formation, the crackformation in the substrate is reduced even at a relatively large filmthickness in comparison with a case where the same film thickness isformed with a smaller number of film formations with a screen plate of200 or 150 mesh, so that the crack generation is substantially zero evenat a thickness of notch of 14 μm as in the present example.

Such result is presumably ascribable to a smaller strain energyresulting from the shrinkage at the baking, due to a smaller volume ofthe wiring at the baking step.

EXAMPLE 8

In the following there will be explained an example of applying theaforementioned wiring substrate to an image display apparatus. In thepresent example 8, there were prepared an electron source substrate andan image display apparatus utilizing surface conductionelectron-emitting devices.

The wiring in the present example was provided with line-shaped notchessubstantially parallel to the longitudinal direction of the wiring asschematically shown in FIG. 1A, in which shown are a notch 12, a wiring11 and a substrate 13. FIG. 1G is a schematic cross-sectional view in aportion indicated by an arrow in FIG. 1A. In FIG. 1G, W indicates thegap of the notches, and T indicates the thickness (distance from thesurface of the substrate to the bottom of the notch) of the notch.

The notches were so prepared that the gap “W” does not exceed 100 μm,and the thickness is without a range from 30 nm to 10 μm.

In the following there will be explained, with reference to FIGS. 3A to3D, 16A, 16B, 17A, 17B, 18A, 18B and 19, the process for preparing theelectron source substrate and the image forming apparatus of the presentexample.

(Step 1)

As shown in FIG. 16A, on a sufficiently rinsed glass substrate 13,paired electrodes 2, 3 were formed in 1000 sets in the X direction and5000 sets in the Y direction.

However, in FIGS. 16A to 18B, for the purpose of simplicity, theelectron-emitting devices are illustrated only in 9 units, namely 3units in the X direction and 3 units in the Y direction.

In the present example, the electrodes 2, 3 were composed of platinum.The electrodes 2, 3 were prepared with a photolithographic method with agap of 20 μm therebetween.

(Step 2)

On the entire surface of the substrate 13 or 200 constituting a rearplate bearing the electrodes 2, 3, photosensitive paste was coated anddried in the same manner as in the example 1 to form a layer of thephotosensitive electroconductive paste (photosensitive electroconductivepaste 14) (cf. FIG. 3A).

The photosensitive electroconductive paste employed in the presentexample was similar to that in the example 1 and contained Ag particlesas the conductive material, acrylic resin constituting a photosensitiveorganic material to be hardened by reaction with ultraviolet light,glass filler etc.

(Step 3)

Then, as in the example 1, the dried layer (photosensitiveelectroconductive paste 14) was irradiated (exposed) with ultravioletexposing light 19 through the light-shielding mask 23 having pluralstriped apertures (cf. FIG. 3B).

(Step 4)

Then the substrate 13 constituting the rear plate was rinsed with anorganic solvent to eliminate (development) of the unexposed portion ofthe photosensitive electroconductive paste layer 14, whereby a developedpattern was formed (cf. FIG. 3C). The developed pattern had notchesformed as shown in FIG. 3C.

(Step 5)

Then the rear plate was baked to form 5000 lower wirings 11, each havingplural notches 12, as shown in FIGS. 3D and 16B. In this step, therow-direction wiring (lower wiring) 11 covers a part of the electrode 3,whereby achieving electrical connection of the electrode 3 and the rowwiring 6. The lower wiring 11 had a height of 15 μm, a gap W of 40 μmbetween the notches and a thickness T of the notch of 6 μm.

(Step 6)

Then insulating paste containing glass particles and a binder was coatedby the screen printing method on each crossing point of the alreadyformed column wiring 11 and the row wiring (upper wiring) 17 to beformed in a next step and baked to form the insulation layer 16 (FIG.17A).

(Step 7)

Then paste containing Ag particles and a glass binder was coated in aline pattern by the screen printing method as in the example 1 and wasbaked to form 1000 row wirings 17 each having plural notches 12 (FIG.17B). In this step the row wiring 17 covers a part of the electrode 2thereby forming connection between the electrode 2 and the tow wiring17.

The screen printing in the step 7 was conducted with a screen plate 18of 150 mesh (cf. FIG. 3C). The screen plate 18 was provided with twoslits of a gap of 100 μm as a pattern for forming the notches.

In this manner there were prepared, on the substrate 13, the lowerwirings 11 with notches, the insulation layer 16 and the upper wirings17 with notches, thus constituting a matrix wiring.

(Step 8)

Then, aqueous solution containing Pd (hereinafter called ink) wasapplied to the gaps between all the electrodes 2 and 3, and was baked inthe air of 350° C. to form an electron-emitting electroconductive film 7consisting of PdO (FIG. 18A).

In the present example, the aforementioned ink was applied by an ink jetapparatus of piezo type, which is one of the ink jet methods. Also thepresent example employed, as the Pd-containing ink, aqueous solutioncontaining 0.15% of an organic Pd compound, 15% of isopropyl alcohol, 1%of ethylene glycol and 0.05% of polyvinyl alcohol.

Through the above-described steps, there was prepared an electron sourcesubstrate (rear plate) prior to forming.

(Step 9)

The electron source substrate prior to forming, prepared in thepreceding step, was placed in a vacuum chamber, and, after the interiorof the chamber was evacuated to a pressure of 10⁻⁴ Pa, there wasexecuted a “forming step” of maintaining the column wirings 6 at 0Vwhile applying a pulse voltage in succession to the row wirings 4 underthe introduction of hydrogen, thereby causing a current in eachelectron-emitting conductive film 7 and forming a gap in a part thereof.

In the forming step, a constant voltage pulse of 5 V was applied inrepetition.

The voltage had a triangular wave form having a pulse width of 1 msecand a pulse interval of 10 msec. The electric forming process wasterminated when the resistance of the electron-emitting conductive film7 reached 1 MΩ.

(Step 10)

The device after the forming step was subjected to an activation step.

More specifically, after the interior of the chamber was evacuated to apressure of 10⁻⁶ Pa, there was executed an “activation step” bymaintaining the column wirings 6 at 0 V while applying a pulse voltagein succession to the row wirings 4 under the introduction ofbenzonitrile with a pressure of 1.3×10⁻⁴ Pa. This step formed a carbonfilm in the gap of the electron-emitting conductive film 7 formed by theforming step and on the films in the vicinity of the gap, therebyforming an electron-emitting region 8 (FIG. 18B).

In the activation step, a rectangular pulse voltage with a pulse heightof 15 V, a pulse width of 1 msec and a pulse interval of 10 msec.

Through the above-described steps, there was prepared an electron sourcesubstrate (rear plate) bearing a plurality of electron-emitting devices.

The evaluation of the electrical properties of such electron sourcesubstrate proved sufficient insulation between the lower wiring 11 andthe upper wiring 17.

In the following there will be explained the method for preparing a faceplate 86 shown in FIG. 19.

(Step 11)

At first a face plate substrate 83 composed of a material same as thatof the substrate 13 for the rear plate was sufficiently rinsed anddried. Then a black member was formed on the substrate 83 by aphotolithographic process.

The black member was formed in such a grating manner as to have anaperture corresponding to a portion where the phosphor of each color ispositioned. The black member has a pitch in the Y direction same as thatof the column wirings 6, and has a pitch in the X direction same as thatof the row wirings 4.

(Step 12)

Phosphors of red, blue and green colors are formed by the screenprinting method in the apertures of the black member.

(Step 13)

On the black member and the phosphors, there was formed a filming layer,by coating solution of polymethacrylate resin in an organic solvent bythe screen printing method and by drying.

(Step 14)

On the filming layer, an Al layer was formed by evaporation.

(Step 15)

Then the face plate 86 was heated to eliminate the resin contained inthe phosphor paste and the filming layer, thereby obtaining a face plate86 in which an image forming member 84, which is a phosphor layerconsisting of the phosphors and the black member, and a metal back 85were formed on the substrate 83.

(Step 16)

Between the substrate 200 of the rear plate formed by the aforementionedsteps and the face plate 86, there were positioned an outer frame 82provided in advance with a spacer (not shown) and a jointing member.

Then, after the face plate 86 and the substrate 200 of the rear platewere sufficiently aligned, heat and pressure were applied in vacuum tosoften the jointing member, thereby adjoining the constituent members.Such step provided an envelope (display panel) 88 constituting, as shownin FIG. 19, an image forming apparatus of which the interior ismaintained in high vacuum.

At the end portions of the wirings 11, 17 extracted from the interior ofthus obtained display panel 88, there was connected a drive circuitthrough a flexible cable, and a moving image was displayed byline-sequential scanning.

In such moving image display with the display panel 88, an image of avery high definition and a high luminance was obtained over a prolongedperiod. Also in the connection of the flexible cable to the leadportions of the upper wirings 17 and the lower wiring 11, there was notgenerated any defect in the wiring. Also there was not generated anypixel defect presumably resulting from a discharge phenomenon.

As explained in the foregoing, the use of the wiring substrate explainedabove allowed to suppress the generation of the end crack, side crackand peeling of wiring.

Therefore, in the lead portion of the wirings, there could be preventedthe drawback that a flexible circuit board or a tab cannot be mounted bypeeling thereof together with the wiring at the succeeding mountingoperation, and also in other portions, the drawback of shortcircuitingwith other portions could be avoided because the end portion of thewiring is no longer bent up, and also because the wiring is no longerchipped nor drops, and also the drawback of instability in the shape ofmarkers such as an alignment mark was also avoided. Furthermore, also ina portion distant from the end of the substrate, the wiring is notpeeled off and becomes floating from the substrate because the substrateno longer generates cracks, whereby the reliability of the product issignificantly improved.

EXAMPLE 9

In the foregoing examples, the recesses are formed in the substantiallyentire area of the wiring in the longitudinal direction thereof. In thepresent example, the recesses are formed only in a part of the wiring inthe longitudinal direction thereof, particularly in the end portions inthe longitudinal direction.

FIG. 20 shows an example of such configuration.

In FIG. 20, there are shown a substrate 13, a wiring 11, and a notch 12provided therein. In order to reduce the resistance, the wiring 11 ismade wider in the vicinity of the end portion (lead portion of thewiring) than in the central portion. The width of the wiring 11 at thecentral portion is 90 μm, and expands on both sides with an angle of 45°to reach 300 μm at the end portion. Except for the vicinity of the endportion, the recess is not provided because the wiring is narrower andis less apt to generate peeling. In the vicinity of the end portion,three notches are so provided as to equally divide the width of the endportion. The wiring has a thickness of 18 μm except for the notchportion and a thickness of 7 μm in the notch portion.

As shown in this example, the recesses may be suitably positioned onlyin the necessary positions.

OTHER EXAMPLES

In the foregoing there have been explained example of forming the wiringon the substrate, but the present invention is also applicable to otherforms such as a rib to be formed on a substrate.

As explained in the foregoing, the present invention allows to suppressgeneration of a crack in the substrate or of peeling of the fine line,by providing the surface of the fine line with a recess for dispersingthe internal stress.

1. A method for forming an electroconductive wiring having recesses, themethod comprising: a step of forming a first film comprising aphotosensitive paste containing metal; a step of irradiating the firstfilm with light through a first photomask bearing a line-shaped aperturepattern which corresponds to the shape of the electroconductive wiring;after the step of irradiating, a step of forming a second film over thefirst film, wherein the second film comprises a photosensitive pastecontaining metal, and the second film together with the first film is toform at least a part of the electroconductive wiring; a step ofirradiating the second film with light through a second photomaskbearing a line-shaped aperture pattern having a plurality of line-shapedapertures arranged in parallel; a development step of developing thefirst and second films irradiated with light; and a baking step ofbaking the first and second films irradiated with light which wasdeveloped in the development step in order to form the electroconductivewiring, wherein the electroconductive wiring has a surface on which aplurality of line-shaped recesses are arranged in parallel.
 2. Themethod according to claim 1, wherein the development step is performedto develop the first and second films irradiated with light, after thestep of irradiating the second film.
 3. The method according to claim 1,wherein the development step includes a step of developing the firstfilm irradiated with light, and a step of developing the second filmirradiated with light, and the step of forming the second film isperformed after the step of developing the first film irradiated withlight.
 4. The method according to claim 3, wherein the baking stepincludes a step of baking the developed first film, and a step of bakingthe developed second film, and the step of forming the second film isperformed after the step of baking the developed first film.
 5. Themethod according to claim 1, further comprising: a step of forminganother film comprising a photosensitive paste containing metal, whereinthe another film together with the first and second films is to form atleast a part of the electroconductive wiring; and a step of irradiatingthe another film with light through a photomask bearing an aperturepattern which corresponds to the shape of the electroconductive wiring,wherein the step of forming another film and the step of irradiating theanother film with light are performed before the step of forming thefirst film.